It depends upon exactly what your interpretation of "grounding" is. If you are experiencing buzzing at mains frequency through the amp then there perhaps is a grounding problem. Touching the strings, bridge, etc usually makes the buzzing worse or better (as opposed to touching the strings when there's no grounding problem, which has no effect because there's no buzz in the first place!!!).

Can I suggetst the following:?

Make sure the amp is OK. Try your bass on another amp and try another bass on your amp.

Make sure the guitar lead is OK. Try another lead with your amp and bass.

If the amp is meant to be grounded at the mains, make sure it is: consult a qualified electrician on this one.

If the bass is the problem then take it to a guitar tech / friendly elecrtonics man for it to be checked.

If you prove it's the bass you'll have to take it apart.

There should be a connection between the outer of the jack socket and the bridge and strings. BUT BE CAREFUL HERE. Most usually that connection is just a piece of wire that runs from the ground side of the electrics to the bridge. But sometimes a resistor / capacitor network is used to make that link which will make an ohm-meter reading apparently wrong: perhaps 100Kohm to perhaps 220Kohms instead of zero ohms. I'm sure the maker of your bass will tell you which system is used.

The way the connection is made to the bridge is usually nothing more sophisticated than trapping the bare wire end under the bridge then the bridge is screwed down onto it. I know of two Precision players who experienced bad grounding problems because the wire became sunk into the body and lost the connection to the metal bridge. Sometimes, too, the wires become oxidized so loosing the connection.

You might like to try the idea of soldering that wire onto a small piece of shim brass to increase the surface area, then rescrew the bridge.

Make sure, too, that all the control pot cases are properly grounded if they should be.

I know of a Washburn guitarist who has similar problems: it turned out to be a faulty pup selector switch.

The ideal is for all pots to have their housings connected to the earth, the cavity to be painted in conductive paint or lined with conductive copper foil, including the cavity cover, and a wire running from the paint or foil to the earth. Some boutique makers even paint the pickup routing holes with conductive paint and run a wire from that to earth. Early Fenders had brass strips under the pickups which were an attempt at shielding. Copper sheilding foil is available from DiMarzio, Stewart MacDonald and probably others.

Any tin foil would probably do the trick in the shielding business, I think. A wire from the input jacks negative pole (shielding) to the bridge usually does quite a bit. If you already have a cable there make sure it is in contact with the stuff it is supposed to be in contact with. Or change it altogether. Good Luck!

Conductive paint - the pukka stuff - is very expensive: it's actually metallic silver made into a paint. A cheaper alternative is (the relatively new) graphite spray which is used in the electrical / electronics industry for electrical shielding. Obviously, to avoid messing up your axe, it's best to spray the stuff into a container then paint it into the bass' control cavities.

Aluminium and copper foil is available with adhesive backings. I'd go for copper because you can solder to it.

Some faults appearing to be grounding faults come from open circuit wiring, pups, etc, rather than the ground being at fault.